1. Field of the Invention
Water-soluble, particularly cationic vinyl polymers are employed on a large scale as process expediters for carrying out for instance separating processes in water treatment or waste water purification, respectively, in the paper, coal and ore industries, in oil production or also in the foodstuffs industry. They serve among other things for flocculation, coagulation, retention or de-watering. Despite the usually small quantities used, these water-soluble vinyl polymers often have an importance which is determining in technology.
Manufacture of these polymers according to prior art is carried out by radical homo- or copolymerisation in a homogenous or heterogeneous phase. The homogenous solution polymerisation in water has the disadvantage that even at polymer contents of below 10% by mass, high-viscosity systems are present, which do not permit a further increase in the content of the active ingredient. The low polymer content caused by this in the final product leads to poor space-time yields of the synthesis and to increased transport costs in transport of the products to the user.
Polymerisations in the heterogeneous phase, such for example as the inverse emulsion polymerisation in organic solvents as a carrier phase, give rise in part to considerably higher contents of solid matter. However they have the disadvantage that operation with solvents requires special protective measures and in application of the products, all the solvent is released to the environment. The inverse suspension polymerisation in hydrophobic combustible solvents as a carrier phase in fact after isolation and drying of the polymers leads to pulverulent products; the multi-stage process however is cost intensive and requires much energy.
2. Description of the Related Art
Due to the disadvantages of a polymerisation in the heterogeneous phase with organic solvents, the manufacture of dispersions of water-soluble polymers was therefore proposed, omitting organic solvents as carrier phase. The documents CA 2 096 472 and U.S. Pat. No. 5,403,883 describe the polymerisation of a combination of water-soluble and hydrophobic vinyl monomers, if necessary in combination with an amphiphatic monomer, in the presence of a polyalkylenether or of a polyelectrolyte, which is incompatible with the polymer to be dispersed, and has molecular weights of &lt;5.times.10.sup.5 g/mol. The polyalklylenether or the polyeletrolyte serves in this case as a dispersion stabiliser. Preferably, poly(diallyldimethylammonium chloride) is used. The resultant dispersed polymer has molar masses of at least 10.sup.6 g/mol. A disadvantage in the methods disclosed in CA 2 096 472 and U.S. Pat. No. 5,403,883 is that considerable quantities of dispersion stabilisers, even up to 80% by mass with respect to the totality of monomers used, are brought into play. Furthermore, during the polymerisation, viscosity maxima can occur, so that the viscosity of the polymerising system under certain circumstances is greater than the viscosity of the polymerised end product.
The document EP 0 183 466 describes the polymerisation of water-soluble monomers in aqueous solutions of inorganic salts in the presence of polyols with molecular weights of up to 600 g/mol and/or polyelectrolytes which have been obtained by homopolymerisation of ionic vinyl monomers or their statistical copolymerisation, as dispersion stabilisers.
The document U.S. Pat. No. 4,380,600 describes the copolymerisation of water-soluble and water-insoluble vinyl monomers to form water-soluble copolymers in aqueous solutions of inorganic salts or with addition of the salt after termination of the reaction. There are used as dispersion stabilisers water-soluble polymers with molar masses between 300 and 10000000 g/mol, which preferably contain in their structural unit an ether, hydroyl or carboxyl group, for example polyethylene glycol, polyethylene oxide or polyvinyl alcohol.
A disadvantage in the methods described in EP 0 183 466 and U.S. Pat. No. 4,380,600 is in particular that the viscosity of the resultant dispersions is comparatively high. A further particular disadvantage is that during the polymerisation viscosity maxima are passed through, which lie in the range of the viscosity during previous solution polymerisation, and therefore render the process difficult.
A disadvantage in all the methods here named in prior art is that the resultant dispersions coagulate after a relatively short time, and therefore the capacity for storage is restricted.